1. Field of the Invention
The present invention relates generally to a method and apparatus for synchronizing various operations of protective relays in a pilot protective relay system, and more particularly to method and apparatus for synchronizing simulation signals generated between protective relays to perform a relay opposed test in a pilot protective relay system or a method and apparatus for synchronizing samples of amounts of electricity in protective relays.
2. Description of the Related Art
A pilot protective relay system is known, in which amounts of electricity (e.g., detected current, voltage and phase) and a relay operation condition signal (e.g., a signal for opening or closing a breaker) are transmitted to an opposite relay system via a transmission system among a plurality of electric-supply stations, located remote from each other, and in which electric transmission lines connecting the electric-supply stations are protected.
The pilot protecting relay system is subjected to an adjustment test in a field, including a relay opposed test, before an actual operation, in order to confirm whether a protecting relay is operating normally.
FIG. 7 shows a pilot protective relay system provided in a power system and a relay opposed test apparatus for executing a relay opposed test. An electric-supply station A and an electric-supply station B are connected to each other via breakers 2A and 2B and an electric transmission line 3. A protective relay 4A is provided in the electric-supply station A and a protective relay 4B is provided in the electric-supply station B. The protective relays 4A and 4B can transmit an electricity amount signal or the like to each other through transmission apparatuses 5A and 5B and a transmission path 6.
When a relay opposed test is performed using the electric-supply station A as a master station, a relay opposed test apparatus 10A supplies a starting signal to a relay tester 7A for generating a simulation signal input to the protective relay 4A, and a relay opposed test apparatus 10B, which receives a test starting command signal from the relay opposed test apparatus 10A, supplies a starting signal to a relay tester 7B for generating a simulation signal input to the protective relay 4B.
The relay testers 7A and 7B input a simulation signal (simulated voltage or simulated current), corresponding to the details of an accident, to the protective relays 4A and 4B. The simulation signal input to the protective relay 4A or 4B from the relay tester 7A or 7B is transmitted, as an electricity amount detected in one electric facility A or B, to the protective relay 4B or 4A of the other electric-supply station, through the transmission apparatus 5A, the transmission path 6 and the transmission apparatus 5B. The protective relay 4B or 4A judges whether an accident has occurred, using the simulation signal received from the protective relay 4A or 4B of the other electric-supply station and the simulation signal supplied from its own relay tester 7A or 7B. For example, when the simulation signal is an accident simulation signal which simulates an internal accident of the electric transmission line 3, if the protective relay 4A or 4B is operating normally, it will detect an accident as a result of an accident detecting operation and output a trip command to open the breaker 2A or 2B. On the other hand, when the simulation signal simulates a normal measurement or an external accident outside the electric transmission line 3, if the protective relay 4A or 4B is operating normally, it will neither detect an accident and nor output a trip command to open the breaker 2A or 2B. In this manner, whether the protective relays 4A and 4B are operating normally can be tested.
When the relay opposed test is executed in the pilot protective relay system, it is necessary to take account of a transmission delay time of a test starting command signal transmitted through the transmission path 6X, since the pilot protective relay system has a structure of detecting an accident using amounts of electricity simultaneously measured at the electric-supply stations A and B.
The relay opposed test apparatuses 10A and 10B are provided in order to generate a simulation signal in consideration of the aforementioned transmission delay time. When a test starting command signal is output from a starting command signal output circuit 11 in the relay opposed test apparatus 10A of the electric-supply station A serving as a master station, the signal is transmitted through the transmission path 6X to the relay opposed test apparatus 10B of the electric-supply station B. In the relay opposed test apparatus 10A, a delay circuit 14 delays the test starting command signal by a time corresponding to the transmission delay time of the transmission path 6X and outputs the delayed signal to a starting circuit 15A. Two starting circuits 15A and 15B output starting signals at the same timing to the relay testers 7A and 7B. As a result, the relay testers 7A and 7B are simultaneously activated so as to generate a simulation signal in order to confirm overall reactions of the pilot protective relay system including the transmission system.
However, the relay opposed test apparatus of the pilot protective relay system requires the transmission path 6X for transmitting a test starting command signal from the master electric-supply station to another electric-supply station. Since a transmission path connecting electric-supply stations is inevitably long, it requires a considerable amount of cost.
In addition, since the relay opposed test apparatus requires the delay circuit 14 for correcting a transmission delay time of the transmission path 6X, the apparatus must be large in size. Further, it is necessary that the transmission delay to be set in the delay circuit 14 be measured accurately.